Abstract: Monochromatic infrared radiation of variable wavelengths between 1.0 and 3.5 microns is directed upon a portion of a moving web, and the spectra of infrared radiation reflected from the web portion and of radiation transmitted through the web portion are separately measured by sensors located on both sides of the web. These spectra are combined to provide an absorption spectrum insensitive to any elastic scattering that is also present. Measures of the contents of the web constituents are generated by least-square fitting the individual absorption spectra of the constituents to the measured absorption spectrum of the web. Means for calibrating the reflectance and transmittance measurements and for keeping the sensor viewing windows free of dirt and dust are also disclosed.

Abstract: Apparatus for measuring the color, brightness and opacity of a moving web in which light from a plurality of sources is directed towards and through a moving web. Light reflected from the surface of the web is conveyed by a plurality of light pipes to a first photodetector array located at a point remote from the web. A circular variable bandpass filter varies the wavelength of the radiation reaching the detector substantially continuously through the optical spectrum to produce a detector output which periodically scans the optical spectrum. The detector outputs at various wavelengths are weighted by a microcomputer to produce brightness and X, Y and Z tristimulus values. Light transmitted through the web is conveyed by a plurality of light pipes to a second photodetector array also located at a point remote from the web. The photodetector is also monitored by the microcomputer to provide an indication of the opacity of the web.

Abstract: Apparatus for measuring and controlling the color of a moving web in which a circular variable bandpass filter having a passband varying substantially continuously with angular displacement through the optical spectrum is interposed in the optical path between the web and a detector and is rotated to produce a detector output which periodically scans the optical spectrum. In one disclosed embodiment, the detector outputs at the various wavelengths are weighted to produce X, Y and Z tristimulus values while, in another disclosed embodiment, dye flows are so controlled as to minimize the total square error between the measured reflectance spectrum and the desired reflectance spectrum.

Abstract: Apparatus for determining the content of moisture or other substance in a material by measuring its relative reflectance at two infrared wavelengths. A chopped radiation beam is produced by arranging a tuning fork such that an oscillating element alternatively moves first and second spaced optical bandpass filters having first and second passband wavelengths into position to intercept a beam of source radiation. The chopped beam is directed on the material being analyzed, and radiation reflected therefrom is applied to a radiation detector. The relative transmittances of the filters at their passband wavelengths are such that the radiation detector generates alternating pulses of equal amplitude for a material having a specified content of the substance. The tuning fork also includes a third filter of zero transmittance which periodically interrupts the beam of source radiation so that the detector provides a background signal which is used to correct the amplitudes of the alternating pulses.

Abstract: In a multi-stage bleaching system in which respective bleaching chemicals are added to the stock in various stages, apparatus in which in the first stage in which chlorine is added to the brown stock, the first of a pair of sensing units associated with the stage comprises a source of red light directed onto the incoming brown stock and a suitable detector for sensing light scattered from the stock to produce a first signal representative of the brightness of the incoming stock and the second similar sensing unit of the pair senses the brightness of the stock immediately following the addition of chlorine to produce a second signal. The first and second signals are compared to produce a difference signal indicative of the change in brightness independently of the condition of the incoming stock and this difference signal is compared with a set point standard to provide a control signal for regulating the addition of the chlorine to the brown stock.